In marking systems such as xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner being electrostatically attached to the latent electrostatic image areas creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material such as paper and the toner image is fixed thereto to form a permanent record corresponding to the original.
In these electrostatic marking systems, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the xerographic process. Sometimes the photoreceptor is in the form of an endless belt and in other systems in the form of a drum. Since the photoreceptor surface is reusable when the toner image is transferred to a final support material such as paper, the surface of the photoreceptor is cleaned and prepared to be used once again in the copying process. In this endless path, several xerographic-related stations are traversed by the photoconductive belt or drum.
In these type of systems, after the transfer station, a photoconductor cleaning station is next. This cleaning station may comprise a cleaning brush and subsequent to the brush is positioned a spots cleaning blade or doctor blade which is used to remove residual debris from the belt. Toner particles, toner additives, machine wear debris, paper fillers or coatings and other contaminants can create film on the photoconductor surface. Also, a film or debris can be generally caused by the toner or toner additives being impacted onto the belt by the cleaning brushes.
“Blade cleaning” is a technique for removing toner and debris from a photoreceptor. In a typical application, a relatively thin metal or elastomeric blade member is supported adjacent to and transversely across the photoreceptor surface with a blade edge that chisels or wipes toner from the surface. Toner accumulating adjacent to the blade is transported away from the blade area by a toner transport arrangement or by gravity. Blade cleaning, generally, is advantageous over other cleaning systems due to its low cost, small cleaner unit size, low power requirements and simplicity. However, conventional blade-cleaning systems suffer from short blade life due to early, random failures in addition to short photoreceptor life due to excess abrading by the blade.
Photoreceptor surfaces can accumulate films that cause print quality degradation and limit the useful life of the photoreceptor. The films may be composed of particulate material that is ground into or smeared on the surface of the photoreceptor. Toner particles, toner additives, machine wear debris, paper fillers or coatings and other contaminant particles can create films. Other films may be due to interactions between the photoreceptor surface and chemicals in the machine environment. Effluents generated by the photoreceptor charge devices are a common source of chemical interactions as well as environmental contaminants that can cause lateral charge migration (LCM) defects. Standard countermeasures to films are to reduce or eliminate the source of the film or to remove the film by increasing abrasion of the photoreceptor surface. In many cases, it is difficult or impossible to reduce the filming source to the point where no print defects are ever generated. Photoreceptor surface abrasion for film removal is difficult to perform in a controlled manner and in all cases reduces the useable life of the photoreceptor.
In many xerographic print systems, the useable life of the photoreceptor (P/R) is a critical factor in determining the overall running cost of the printer. There are at least two primary failure modes for most photoreceptors. The first is the degradation in function due to electrical and mechanical wear of the photoreceptor surface. A second failure mode is the accumulation of contaminants or films on the surface of the photoreceptor. Depending on the operating conditions of the xerographic engine, either of these two failures modes can be more or less dominant. These operating conditions would include, but are not limited to, document area coverage, media type, ambient temperature and relative humidity. Thus, balancing the two P/R failure modes is typically key to managing the run cost for the xerographic engine.
In printing architectures that utilize blade cleaners, the working angle of the cleaning blade typically impacts the rate of photoreceptor wear. Because of this, the blade working angle can be used as a means for actively adjusting the rate of surface wear on the photoreceptor. The blade angle provides a means for balancing the amount of photoreceptor wear and the buildup of films. At higher working angles, usually there is faster photoreceptor P/R wear but also less filming. At lower working angles, usually there is a higher degree of filming but substantially less wear of the photoreceptor surface.
By actively adjusting the blade working angle, it is possible to trade off the rate of P/R wear with the degree of filming. With a known latitude boundary for the acceptable level of filming, the goal would be to steer the working angle as low as possible thereby minimizing the photoreceptor wear rate while maintaining acceptable levels of film accumulation.
Film generation rates will vary based on xerographic system parameters and uncontrolled environmental and usage parameters. Because of these variations, it is very difficult to predict the resulting accumulated film thickness. When the accumulated film thickness is below the threshold acceptable film limit, the blade can be operated at low working angles. Low working angles maximize photoreceptor life by minimizing photoreceptor wear. As the film thickness approaches or reaches the acceptable limit, the blade working angle is increased to thereby increase photoreceptor wear. The additional wear reduces the film thickness to maintain acceptable film thickness and acceptable images.
To optimize photoreceptor life, the film thickness as indicated by a sensor or sensors is held at the maximum acceptable limit. In this condition there would be no print defects due to filming and photoreceptor life would be maximized by operating the blade at high working angles only as often as necessary to prevent film thickness rising to unacceptable levels. The blade working angle would be adjusted to match the film removal rate to variations in the film generation rate so that the film thickness is maintained at the acceptable limit.